The present invention generally relates to pressure-sensitive mats and particularly relates to pressure-sensitive mat systems that include detachable mat cables.
A typical pressure-sensitive mat includes one or more normally separated electrode pairs encased in a sealed, flexible material. Downward force on the mat's upper surface forces the electrodes into contact with each other, which causes an electrical “closure” through the normally open mat electrodes. Some mats include one large electrode pair comprising vertically stacked upper and lower conductive sheets separated by one or more compressible spacers, while other mats include multiple, smaller electrode pairs. Of course, other sensing technologies may be used, such as resistive or capacitive sensing, but the underlying weight-based actuation principle remains essentially unchanged across mat varieties.
Pressure-sensitive mats find use in a variety of applications, ranging from automatic door actuation to hazardous machine guarding. In that latter context, such mats often are referred to as “safety mats.” Typically, safety mats cover the floor areas in and around dangerous work locations and thus provide a reliable and robust mechanism for detecting the presence of persons or vehicle in those locations. For example, a safety mat may be electrically wired to a “mat controller” that is configured to shut down hazardous equipment upon sensing a closure of the mat's electrodes. Safety mats also may be used to ensure that an operator remains in a safe operating location by placing a mat at the designated location and configuring an associated mat controller to permit machine operation only when weight is sensed at that location.
Conventionally, rigid perimeter frames (mat trim pieces) fasten to the floor and hold mats in place, i.e., the frames prevent the positioned mats from sliding or shifting from their desired floor locations. Such frames may be beveled to minimize the tripping hazard posed by mat edges, and may provide for joining smaller mats into a larger mat grid. In such applications, the trim strips themselves may be “active” in that they provide for pressure sensing along the seams between adjacent mats. Active trim strips eliminate or at least minimize “dead” areas between co-joined mats. Trim strips also may include internal cable raceways that allow mat cables to be routed within them. Such internal routing further reduces tripping hazards and provides significant protection for the cables that interconnect the mats to the mat controller(s).
To complement the almost universal use of mat trim strips, mat cables normally are permanently connected to the mats in a manner that minimizes cable termination protuberances along mat edges. Molding the mat-to-cable termination into the mat itself avoids the need for bulky cable terminations at the mat's edge, e.g., terminal blocks or the like, that would disrupt the mat's dimensional envelope and thus prevent the use of edgewise flush mat trim strips.
Integrally molded mat-to-cable terminations offer additional advantages, such as the opportunity to securely attach the cable wires to the mat's internal electrodes via connections made within the mat's sealed body. Such connections inherently are watertight, assuming that the molded cable inlet is sealed. Further, internal connections inherently are less vulnerable to damage because they are isolated from the foot and vehicle traffic to which the mat's exterior is exposed.
However, substantial disadvantages accompany the use of integral mat cables. For example, mat purchasers usually must order mats based on the desired cable length and, in turn, mat manufacturers usually must stock mats having many different cable lengths, or be prepared to custom-fill orders based on the requested cable length. Of course, mat cables may be cut or spliced, but such modifications decrease the overall safety integrity of mat systems by adding additional connection failure points that are vulnerable to mechanical damage, water ingress, corrosion, etc.
An ideal pressure-sensitive mat system would combine the advantages of integral cables with those of detachable cables, while simultaneously avoiding the attendant mechanical and safety disadvantages of detachable cable connections. With that approach, the manufacturing and use of pressure-sensitive mats would be simplified because the cable length variable would be independent of the basic mat configuration. Mats could then be manufactured and ordered according to desired mat sizes without regard to the widely varying lengths of mat cables used in particular installations. Further advantages would be gained in that mats and mat cables become independently replaceable items, thereby simplifying maintenance and repair of mat systems.